Brazed heat exchanger

ABSTRACT

A brazed heat exchanger having a stack of heat exchanger plates, each with an inflow hole and an outflow hole, that are arranged such that closed and open flow ducts for different media alternate in a stack direction. In the open flow ducts are two endpieces with a hole whose edge extends around the inflow hole or around the outflow hole respectively. The endpieces are deformed metal sheets with corrugations that form ducts, The metal sheets include flow openings for the medium flowing through the open flow ducts. The hole edges are deformed and have a height approximately corresponding to a height of the open flow duct, and are arranged close to a rim hole of the inflow hole or of the outflow hole.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application No. 102014 005149, filed Apr. 8, 2014, the entire contents of which are herebyincorporated by reference herein.

BACKGROUND

The present invention relates to a brazed heat exchanger which isarranged in a housing and which has a stack of heat exchanger plates.

Alternating closed and open flow ducts, and the arrangement of the stackin a housing, signify a specific generic type of heat exchangers, whichdiffer from known heat exchangers without a housing and with exclusivelyclosed flow ducts inter alia in that the heat exchangers discussed herehave only two openings in the heat exchanger plates, whereas the otherheat exchangers have at least four openings. Said openings in the platesof both generic types of heat exchangers provide inlet and outlet ductsextending vertically through the stack.

Endpieces are metal parts which are inserted into the flow ducts andwhich occupy only a small part of the flow ducts. The endpieces occupyonly two opposite ends of the flow ducts. In the case of approximatelyrectangular heat exchanger plates, these are generally the relativelyshort sides of the plates or of the flow ducts formed by means of theplates.

A heat exchanger of the specific generic type is known from EP 470 200B1. Said heat exchanger is situated in a housing (not shown in saiddocument) with at least one inflow opening and one outflow opening forthe medium flowing through the open flow ducts of the heat exchanger. Inthe known heat exchanger, the endpieces are solid metal plates, thethickness of which corresponds to the height of the flow ducts. Theendpieces have been arranged in the open and in the closed flow ducts.The endpieces firstly considerably increase the weight of the heatexchanger, but secondly lead to an extremely stable heat exchanger whichcan be fastened in the housing in an advantageous manner using the solidendpieces. However, owing to the endpieces, the size of theheat-exchanging surface area is reduced.

Another heat exchanger of said generic type is known for example from EP1 083 398 A1. Said heat exchanger has lamellae which are arranged bothin the open flow ducts and in the closed flow ducts and which increasethe efficiency of the heat exchange. In the case of said heat exchanger,a corrugated sheet-metal strip of circular form has been placed into theclosed flow ducts so as to encircle said openings. Semicircular solidendpieces that have hitherto been provided are thus replaced. A morelightweight heat exchanger, which exhibits higher performance, islikewise realized.

The heat exchangers are brazed in a brazing furnace and subsequentlyinserted into the housing, in which they can perform their function perse.

SUMMARY

One object of the invention consists in providing an advantageousalternative which likewise realizes a relatively lightweight brazed heatexchanger in a housing, with high heat exchange performance, without thestability of the heat exchanger being significantly reduced, wherein thequality of the brazed connections should be ensured.

In one embodiment, the endpieces are deformed metal sheets withcorrugations which form ducts, which metal sheets are provided with flowopenings for the medium flowing through the open flow ducts. Thesheet-metal thickness of the deformed metal sheets approximatelycorresponds to the sheet-metal thickness of the heat exchanger plates.In one exemplary embodiment, said thickness is approximately 0.2-0.5 mm.A deformed hole edge of the hole of the deformed metal sheet has aheight approximately corresponding to a height of the open flow duct.

A braze gap of a size of approximately 0.2 mm is situated between theapproximately vertically standing hall edge and the edge of the inflowhole or of the outflow hole respectively. Such braze gaps impart acapillary action on the molten braze. The edge of the inflow hole and ofthe outflow hole respectively has been deformed. Said edge has rimholes. The rim holes each point into the open flow ducts, in which thedeformed metal sheets are situated. The rim hole of one plate of oneplate pair is connected to a rim hole of the next plate of the nextplate pair. The rim holes have been plugged one inside the other.

It has been identified that such a design not only achieves the desiredperformance improvements and weight reduction but can also provideadvantages in terms of manufacturing in the case of brazed heatexchangers.

The brazing process is performed in a brazing furnace, wherein a weightor a force acts on the heat exchanger during the brazing process. Forthis purpose, the heat exchanger must firstly be preassembled andprepared for the brazing process. It has been found that, in particular,the special hole edge design of the deformed metal sheet and thearrangement thereof close to the inflow hole or to the outflow holerespectively generates stability comparable to that obtained with solidendpieces. Furthermore, it is possible to produce sealed and durablebrazed connections even though the surfaces to be brazed areconsiderably smaller than in the prior art.

A housing, in one embodiment, is a structure which at leastsubstantially encompasses the brazed heat exchanger and which has atleast one inlet for the medium flowing through the open flow ducts andwith an outlet through which the medium passes after flowing through theopen flow ducts. A housing of said type may accordingly likewise beregarded as a flow duct into which the stack of heat exchanger plates,with endpieces in the open flow ducts and with lamellae in the closedflow ducts, is inserted after the brazing process.

Closed flow ducts, in one embodiment, are flow ducts which arecharacterized by a sealed, closed connection extending in encirclingfashion around the edges of in each case two heat exchanger plates andwhich have two holes in the heat exchanger plates, wherein one holeconstitutes an inflow hole, and the other hole constitutes an outflowhole. The closed flow duct is situated in each case between the twoplates that can be regarded as the above-mentioned plate pair.

Since the heat exchanger plates form a stack, inflow holes which are inalignment in the stack give rise to a vertical inflow duct extendingthrough the stack, and the outflow holes in a streamlined configurationgive rise to a vertical outflow duct extending through the stack.

To form the inflow duct, the inflow hole of one plate is connected ineach case to the inflow hole of an adjacent plate of the next plate pairby virtue of an open flow duct arranged in each case in between beingbridged, so as to ensure the separation between the media. The sameapplies with regard to the outflow holes or with regard to the formationof the outflow ducts.

Since the corrugations provide a brazed connection to the in each casetwo plates that delimit an open flow duct, the desired stability is alsoattained, in particular around said inflow and outflow ducts.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section through an inlet or outlet duct of a heatexchanger according to an embodiment of the invention, without showingthe housing;

FIG. 2 shows a detail of an endpiece from FIG. 1;

FIG. 3 shows an endpiece, two of which are arranged in each open flowduct of the heat exchanger of FIG. 1;

FIG. 4 shows a perspective view of the heat exchanger of FIG. 1 situatedin a housing;

FIG. 5 shows the heat exchanger from FIG. 4, in which the upper platesare shown in an exploded illustration;

FIG. 6 shows a longitudinal section through the heat exchanger situatedin the housing of FIG. 4;

FIG. 7 shows a detail of a lamella situated in the closed flow ducts ofa heat exchanger according to some embodiments;

FIG. 8 shows details of relevance with regard to the brazing of the heatexchanger of FIG. 1;

FIG. 9 shows a further one of several possible alternative designs of ahole edge of the endpiece, similarly to FIG. 2.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the accompanyingdrawings. The invention is capable of other embodiments and of beingpracticed or of being carried out in various ways.

DETAILED DESCRIPTION

The brazed heat exchanger of the embodiment shown, which is situated ina housing 40, is an oil cooler by means of which an oil, such astransmission oil, engine oil or the like, is cooled or adjusted to theappropriate temperature by means of cooling liquid. The oil flowsthrough the closed flow ducts 2, and the cooling liquid flows throughthe housing 40 and the open flow ducts 3 of the oil cooler.

Other embodiments (not shown) may be provided which relate to charge-aircooling, exhaust-gas cooling or else to refrigerant cooling orrefrigerant condensation or refrigerant evaporation, to name but a fewfurther advantageous applications.

The brazed heat exchanger arranged in the housing 40 has a stack of heatexchanger plates 1 a, 1 b which are equipped with in each case oneinflow hole 10 and one outflow hole 11. The housing 40 (FIGS. 4-6) canbe closed by means of a cover (not shown) or the like. The housing 40may however also be a so-called cavity of an engine or transmissionhousing, wherein the upper, open side points into the interior thereof.The plates 1 a, 1 b are arranged such that closed and open flow ducts 2,3 for oil and for cooling liquid alternate in a stack direction. In theopen flow ducts 3 only, there are arranged two endpieces 20 which eachhave a hole 21. The edge 22 of the hole 21 of one endpiece 20 extendsaround the inflow hole 10, and the edge of the hole 21 of the secondendpiece 20 extends correspondingly around the outflow hole 11. This canbe seen most clearly from FIGS. 1 and 3 in conjunction with FIG. 4 or 5.

The endpieces 20 are deformed metal sheets with corrugations 24 thatform ducts 23. The thickness of the metal sheets 20 correspondsapproximately to the thickness of the heat exchanger plates 1 a, 1 b.Here, “corresponds” is to be understood to mean that the heat exchangerplates 1 a, 1 b may have for example a metal sheet thickness in therange from 0.2-0.5 mm. The thickness of the endpieces 20 could then forexample even be 0.15 mm or 0.5-0.7 mm in order to still lie in the rangeintended to be covered by “corresponds”. In this connection, it is alsopointed out that the duct height of the open flow ducts 2 may, in apractical exemplary embodiment, be approximately 1.5-3 mm. The closedflow ducts 3 are approximately 2-4 mm high (FIG. 1).

The ducts 23 of the endpieces 20 are provided with flow openings 25 forthe cooling liquid flowing through the open flow ducts 3. The hole edge22 is deformed and has a height h which approximately corresponds to aheight of the open flow duct 3. Large tolerances should not be permittedwith regard to said height h. The hole edge 22 is arranged sealingly, inencircling fashion, against a rim hole 12 of the inflow hole 10 or ofthe outflow hole 11 respectively. This is shown in FIGS. 2 and 3.

As is also shown in said figures, a braze gap 26 is situated between theapproximately vertically standing hole edge 22 and the rim hole 12. Thebraze gap 26 may for example be 0.1-0.3 mm in size. During the brazingprocess, the braze gap 26 will, owing to its capillary action, fill withbraze material and thus ensure sealed and durable connections.

By contrast to FIG. 2, FIG. 9 shows that the deformed hole edge 22 mayalso have an inwardly pointing bent flange 22 a for furtherreinforcement. Reference signs not shown in FIG. 9 may be gathered fromFIG. 2. In FIGS. 2 and 9, the hole edge 22 extends upward from the heatexchanger plate lb, which is at the bottom in the image, to the upperplate la. In further embodiments that are not shown, the hole edge 22extends from top to bottom.

With regard to the said rim holes 12 at the inflow hole 10 and at theoutflow hole 11, it can be seen from FIGS. 1 and 2 that said rim holesengage into one another and bear against one another in oppositedirections. As can be seen, the rim holes 12 connect the closed flowducts 2 to one another and, at the same time, each bridge the open flowducts 3 arranged in between.

Furthermore, it can be seen from FIG. 3 that the ducts 23 of theendpieces 20 have different duct lengths. Some of the ducts 23 areprovided with a curvature. In the exemplary embodiment shown, thecurvature corresponds approximately to a curvature of the hole edge 22.Other, in particular shorter ducts 23 do not have a curvature. Thedirection and form of the ducts 23 may be adapted on a case-by-casebasis.

Some of the ducts 23 are of arcuate form. They extend around a centersituated approximately in the middle of the hole 21. The ducts 23 have aflow opening 25 at the start of the ducts 23 and another flow opening 25at the end of the ducts. In embodiments that are not shown, the ducts 23have been provided with more than two flow openings 25, for example inthe flanks of the undulations 24.

It is of note that the longest of the ducts 23 is situated close to thehole edge 22 and extends around the major part of the circumferencethereof. In this way, in the edge region of the holes—together with thedeformed hole edge 22 described above—adequate stability is provided,which is expedient in particular during the course of the brazingprocess in order to prevent the so-called collapse of the plates 1 a, 1b under the action of the brazing temperature.

The open and closed flow ducts 2, 3 are formed from pairs of heatexchanger plates 1 a, 1 b. The closed flow ducts 2 are situated withinthe plate pairs. The open flow ducts 3 are arranged between the platepairs.

The closed flow ducts 2 are completely filled with a lamella 27 (FIGS.5-7). The corrugated lamellae 27 have offset incisions in thecorrugation flanks and have two openings which correspond to the inflowhole 10 and to the outflow hole 11 respectively.

The open flow ducts 3 are provided, at least outside the regionsoccupied by the endpieces 20, with studs 32 formed into the heatexchanger plates 1 a, 1 b, or with similar turbulence elements.

The studs 32 are formed with a height approximately half that of theopen flow duct 3, with opposite studs 32 being supported and connectedby brazing. In embodiments that are not shown, the studs 32 have aheight corresponding to the duct height, such that said studs can besupported on the opposite planar plate 1 a or 1 b.

The solid heat exchanger of the exemplary embodiment is composed of asuitable high-grade steel. In embodiments that are not shown, analuminium alloy or some other steel is used as material. For the brazingof high-grade steel, use is often made of braze foils or braze pastes,because the coating of high-grade steel sheets with braze containing Cuor Ni is at present associated with high costs.

It can be seen from FIG. 8 that, between one side of the endpieces or ofthe deformed metal sheet 20 and one heat exchanger plate 1 a, there issituated a braze foil 33 which approximately corresponds to thecircumference of the metal sheet 20. It can also be seen that, betweenthe other side of the deformed metal sheet 20 and the other heatexchanger plate lb of the next pair, there is arranged another brazefoil 34 which extend approximately over the entire heat exchanger plate1 b, including the second deformed metal sheet 20. In embodiments thatare not shown, the said braze paste is used instead of the braze foil33.

To save on expensive braze material, the inventors have formed voids inthe other braze foil 34 at the locations at which no brazed connectionis provided. The corresponding voids are denoted by the reference sign35.

The formation of the stack is facilitated by the hole 21 in theendpieces and by the rim holes 12 that correspond therewith. The factthat the form of the lamellae 27—with their two openings—is adapted tothe form of the closed flow ducts 2 (FIG. 5) is also conducive to easierstacking On the stack there are often also situated connection flanges14 which form an elongation of the inlet and the outlet duct 10, 11. Onthe other end of said ducts 10, 11 there are arranged closure disks 13.The stack of heat exchanger plates 1 a, 1 b, endpieces 20, lamellae 27,connection flanges 14 and closure pieces 13 is brazed in a brazingfurnace. After the stack is brazed, it is inserted into the housing 40.

As can be seen from the said FIG. 3, the deformed metal sheets 20 havebeen configured such that they can admit flow from opposite directions.In this case, the performance-increasing advantages are at leastapproximately maintained. This can also be explained on the basis ofFIG. 4 or FIG. 5. The housing 40 has multiple inlets and outlets 41-46.In a practical exemplary embodiment, these will generally not beprovided. In general—but not always—there will be only a single inlet,for example 41, 42 or 43, and a single outlet 44, 45 or 46. It can beseen from FIG. 4 that the endpieces 20 can admit flow or discharge flowin opposite directions indicated by means of the arrows, without theiradvantageous effect being impaired. Inlets and outlets on the housing 40may also be arranged on the top and/or on the bottom, that is to say notin the plate plane as shown in FIGS. 4 and 5, but perpendicular thereto.

In each case two deformed metal sheets 20 arranged in an open flow duct3 are of identical form. In the exemplary embodiment, their shape can beregarded as being approximately D-shaped. Circular metal sheets 20 arelikewise possible. In general, the shape of said metal sheets is adaptedto the plate geometry. The deformed metal sheets 20 have a region inwhich flow is admitted and a region in which flow is discharged. Themetal sheets 20 are arranged such that, in each open flow duct 3, in thecase of the metal sheet 20 arranged at the inlet side, the arcuateregion of the D shape of said metal sheet 20 can be regarded as theregion in which flow is admitted, and the approximately straight,terminating region can be regarded as the region in which flow isdischarged. In the case of the metal sheet 20 arranged at the outletside, the conditions are the opposite, because in the case of said metalsheet 20, the straight, terminating region constitutes the region inwhich flow is admitted, and the arcuate region constitutes, in thiscase, the region in which flow is discharged. The ducts 23, with flowopenings 25, formed in the metal sheet 20 are now arranged such thatapproximately identical conditions with regard to pressure lossesprevail at both metal sheets 20, even though these admit flow fromopposite directions.

Various features and advantages of the invention are set forth in thefollowing claims.

What is claimed is:
 1. A brazed heat exchanger configured to be receivedin a housing and configured to transfer heat between a first medium anda second medium, the brazed heat exchanger comprising: a plurality ofheat exchanger plates arranged to form a stack, each of the plurality ofheat exchanger plates having a thickness and including an inflow holeand an outflow hole, the plurality of heat exchanger plates arranged inthe stack to define a plurality of closed flow ducts between adjacentheat exchanger plates for the first medium and a plurality of open flowducts between adjacent heat exchanger plates for the second medium, theclosed and open flow ducts alternating in a stack direction of theplurality of heat exchanger plates; and first and second endpieces ineach of the plurality of open flow ducts, wherein the first and secondendpieces each include a metal sheet with corrugations that form ducts,each having a flow opening for the second medium flowing through theopen flow ducts, the first and second endpieces each further include ahole having an edge that is deformed such that the edge has a heightapproximately corresponding to a height of the open flow ducts, whereinthe edge of each of the first endpieces extends around the inflow holeand the edge of each of the first endpieces is close to a rim hole ofthe inflow hole, wherein the edge of each of the second endpiecesextends around the outflow hole and the edge of each of the secondendpieces is close to a rim hole of the outflow hole.
 2. The brazed heatexchanger of claim 1, wherein the edge of each of the first endpieces isformed with a braze gap around the inflow hole, and wherein the edge ofeach of the second endpieces is formed with a braze gap around theoutflow hole.
 3. The brazed heat exchanger of claim 1, wherein the rimholes of the inflow hole and of the outflow hole of two of the pluralityof heat exchanger plates forming one of the plurality of closed flowducts engage into one another and bear against one another in oppositedirections.
 4. The brazed heat exchanger of claim 2, wherein the edge ofeach of the first and second endpieces is approximately verticallystanding, wherein the braze gaps of the first and second endpieces arearranged between the approximately vertically standing edge and the rimhole.
 5. The brazed heat exchanger of claim 1, wherein the ducts of thefirst and second endpieces have at least two different duct lengths. 6.The brazed heat exchanger of claim 1, wherein at least one of the ductsof the first and second endpieces has a curvature.
 7. The brazed heatexchanger of claim 6, wherein the curvature corresponds approximately toa curvature of the edge and runs approximately concentric thereto. 8.The brazed heat exchanger of claim 6, wherein at least one of the ductsof the first and second endpieces are of arcuate form so as to extendaround a center, with a flow opening at the start of the duct and a flowopening at the end of the duct.
 9. The brazed heat exchanger of claim 1,wherein a longest of the ducts of the first and the second endpiecesextends close to the edge and around a major part of a circumferencethereof.
 10. The brazed heat exchanger of claim 1, wherein the open andthe closed flow ducts are formed from pairs of the heat exchangerplates, wherein the closed flow ducts are arranged within the platepairs and the open flow ducts are arranged between the plate pairs. 11.The brazed heat exchanger of claim 1, wherein the closed flow ductsinclude lamella.
 12. The brazed heat exchanger of claim 1, wherein theopen flow ducts are formed outside regions occupied by the metal sheetswith studs formed into the heat exchanger plates.
 13. The brazed heatexchanger of claim 12, wherein the studs are formed with a heightapproximately half that of the open flow duct, with opposite studs beingsupported and connected by brazing.
 14. The brazed heat exchanger ofclaim 1, wherein between one side of one of the first endpieces and oneheat exchanger plate, there is situated a braze foil or paste whichapproximately corresponds to a circumference of said first endpiece. 15.The brazed heat exchanger of claim 14, wherein between the other side ofsaid one of the first endpieces and an other heat exchanger plate, thereis arranged another braze foil or paste which extends approximately overthe entire other heat exchanger plate, including one of the secondendpieces.
 16. The brazed heat exchanger of claim 15, wherein the otherbraze foil or paste is situated at least at locations at which brazingis performed, wherein said braze foil or paste has voids at otherlocations where no brazing is performed.
 17. The brazed heat exchangerof claim 1, wherein the metal sheets are configured so as to be able toadmit flow from opposite directions.
 18. A brazed heat exchangerconfigured to be received in a housing and configured to transfer heatbetween a first medium and a second medium, the brazed heat exchangercomprising: a plurality of heat exchanger plate pairs arranged into astack, open flow ducts arranged between adjacent ones of the heatexchanger plate pairs; a vertical inflow duct extending through thestack at a first end of the stack and a vertical outflow duct extendingthrough the stack at a second end of the stack, the vertical inflow andoutflow ducts being fluidly connected by a closed flow duct within eachof the heat exchanger plate pairs to allow for the first medium to flowbetween the vertical inflow and outflow ducts; and a plurality of metalsheets provided within the open flow ducts at both the first end and thesecond end of the stack, each of the metal sheets being joined toadjacent ones of the heat exchanger plate pairs to provide structuralsupport thereto, wherein each of the plurality of metal sheets isprovided with ducts to allow for flow of the second medium around thevertical inflow and outflow ducts.
 19. The heat exchanger of claim 18,wherein the metal sheets are deformed to have corrugations correspondingin height to the open flow ducts arranged between adjacent ones of theheat exchanger plate pairs, the ducts provided within the metal sheetsbeing defined by said corrugations.
 20. The heat exchanger of claim 18,wherein each of the ducts provided within the metal sheets includes aflow opening at the start of the duct and a flow opening at the end ofthe duct, wherein at least some of said flow openings are in fluidcommunication with the open flow ducts arranged between adjacent ones ofthe heat exchanger plate pairs.